In this chapter:

An ocean is a large body of salty water that surrounds large land masses

A desert is an area that receives very little or no rain through the year

Introduction

The previous chapter, Chapter 2: The formation and structure of the Earth, looked at how our planet was formed. It also looked at the Earth's structure. When different materials inside the Earth move they might create earthquakes, volcanic eruptions or movements of the tectonic plates. All these events create and shape the Earth's landforms. This chapter looks at the different types of landforms and how they are formed.

Landforms and the landscape

Tectonic plates move and interact with each other constantly. Their activities lead to earthquakes, volcanic eruptions and the splitting of the Earth's crust. These events change the surface of the Earth by creating different landforms. A landform is a term that describes the shape of a natural land feature. Landforms are created by different forces of nature. For example, mountains, oceans, valleys and deserts can be called landforms. A group of landforms in one area makes up a landscape. The view from an aeroplane or from the top of a hill gives a good picture of a landscape.

Types of landforms

There are many different types of landforms on the Earth. Some of them were formed over millions of years and others were formed in a matter of hours. The formation of a mountain range, for example, would usually take a few million years. Events like earthquakes and volcanic eruptions can 'wipe off' landforms, or form new ones in a matter of hours. Examples of some natural landforms are mountains, oceans, rivers, hills, volcanoes, valleys, desserts, waterfalls, caves and cliffs. This chapter looks at the formation of some major types of landforms.

Mountains

A mountain is a raised part of the Earth's surface. Mountains can be formed in different ways that involve internal (inside) or external (outside) natural forces. The movement of tectonic plates is called plate tectonics. Plate tectonics is an internal natural force because it happens inside the Earth. When tectonic plates collide, they raise the Earth's crust. As mentioned before, tectonic plates move very slowly, so it takes many millions of years to build a mountain. Mountains can also be formed by external natural forces like rain, wind and frost in the process of erosion.

Mountains with shapes that are sharp and jagged are called young mountains. Mountains that have a smoother, more rounded look are called old mountains. The South American mountain range, the Andes, is a young mountain range. Old mountains look smoother because they have been shaped by natural weathering over a longer period of time. The Himalayan Mountains, which are an older type of mountain, are still 'growing' due to plate tectonics.

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If they are given enough time, usually millions of years, all mountains crumble. High, jagged peaks become low, rounded hills. Eventually, mountains wear away, becoming soil and sand.

Valleys

A flat area of land between hills or mountains is called a valley. Valleys are usually formed by river water. The speed at which a river deepens its valley depends on the speed of the flow of the river water and the type of materials from which the river bed (the bottom of the river) is made. Softer and lighter materials are moved by water faster than hard and heavy ones. That means that a river bed made from soft sediments can be changed or deepened faster than a hard and rocky one.

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Oceans

An ocean is a large body of salty water that surrounds a large land mass. After studying different rock, scientists have established that the first ocean on the Earth was formed about 4000 million years ago. Even though early Earth did not have any water, it had the chemical elements that make up a water molecule. Some scientists believe that the Earth's first rain was just cooled-down volcanic steam. Rainwater started to collect in low-lying areas of the Earth's crust, forming the first ocean. Another group of scientists believes that first water was 'delivered' on the Earth by massive ice-bearing comets.

The formation of the first ocean was the starting point for the evolution of life on Earth. Oceans made the Earth's climate milder and more suitable for life. An ancient ocean was the place where the first oxygen-producing algae were formed. Today, more than two-thirds of the Earth's surface is covered with water which is in constant motion. This motion of water currents plays a very important role in shaping landforms.

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Deserts

A desert is an area that receives very little or no rain through the year. Deserts usually form as a result of climate change. Deserts have very dry air and lots of wind. Deserts can be hot or cold. During the daytime the temperature in hot deserts is very high and at night it drops to a few degrees. A cold desert is a desert that has snow in the winter. An example of a hot desert is the Sahara desert. Sometimes people call Antarctica a frozen desert. It has not rained or snowed in some places there for over 100 years. A cold desert never becomes warm enough for plants to grow in it. Deserts cover about a fifth of the Earth's land surface.